It is well known that low resistance ohmic contacts to GaAs are difficult to obtain due to a 0.8 eV Shottky barrier associated with the metal-GaAs interface. It is also known in the art that the metal-InGaAs interface produces a nearly zero Shottky barrier height and hence a low contact resistance. Ohmic contact may be made to GaAs by interposing an In.sub.x Ga.sub.1-x As layer, with x=0 at the GaAs interface and graded to x.apprxeq.0.8 at the metal-InGaAs interface, between the GaAs layer and the metal contact. An advantage of this structure is that post-deposition alloying of the contact is not necessary.
In the fabrication of semiconductor circuits from Group III-V compounds, Au and Au-alloys are the most commonly employed metals for making electrical contact at the device level. Specifically, AuGe/Ni/Au, Ti/Pt/Au, and AuZn are a few of the metallization schemes that have been used to make contact to GaAs as well as to InGaAs. However, as demand for better device performance continues to increase, the need for a lower resistance contact scheme to InGaAs, in particular, has become apparent.